There are a number of applications for a web feed mechanism in which a web material, such as paper, fabric, foil, or the like, must be advanced in controlled steps, each step representing an accurately defined length of the web material. For example, in the labeling and printing arts a continuous web or foil is advanced in unit lengths during an imprinting or die cutting, or other stamping operation, to form a plurality of individual labels or other repetitive lengths of material. Starting, advancing and stopping the web without breaking the web and at the same time controlling the incremental lengths of web to a close tolerance has been a problem. Accuracy and speed require the web to be accelerated and decelerated very rapidly without exceeding the tensile strength of the web material. High torques are required while maintaining inertial loads to a minimum.
The stepper motor has been used as a drive mechanism for advancing web material in controlled steps because the stepper motor can be advanced in accurately controlled angular increments, and because the stepper motor provides substantially full torque when it is not rotating or stepping, thus providing a braking effect. However, stepper motors having sufficient torque to both accelerate and decelerate the foil or web, as well as to accelerate and decelerate the drive mechanism, presents difficulties in the size and cost of the stepper motor and the power capacity of the associated stepper motor control.